The present invention relates to a high-pressure fuel accumulator for a fuel injection system of an internal combustion engine, in particular for a common-rail system.
In a common-rail injection system, a high-pressure pump conveys the fuel to be injected from a tank into a central high-pressure fuel accumulator, which is known as a common rail. High-pressure lines lead from the high-pressure fuel accumulator to the individual injectors associated with the cylinders of the internal combustion engine. The injectors are controlled individually by the engine electronic system as a function of the operating parameters of the internal combustion engine to inject fuel into the combustion chamber of the internal combustion engine. The base body of the high-pressure fuel accumulator is made of a forged blank, for example, with the interior of the base body being introduced as a longitudinal bore into the base body. The base body manufactured in this way is then provided with connecting bores which open into the longitudinal bore. Such a high-pressure fuel accumulator is known from German Published Patent Application No. 196 40 480 A1 (corresponding to U.S. Pat. No. 6,223,726), for example. To adjust the pressure in the high-pressure fuel accumulator as a function of the load state of the engine, a pressure regulating valve is used in the related art; this valve has its own housing part and is connected either to the high-pressure pump or is screwed onto an end connection of the high-pressure fuel accumulator by using screwable fastening means.
One disadvantage of the known high-pressure fuel accumulators is that because of the high pressure in the accumulator space, the sealing sites in the connection area of high-pressure fuel accumulators and pressure regulating valves may need to be manufactured with high precision, and multiple sealing elements may be necessary for the seal. In addition, problems occur at the valve seat of the pressure regulating valve, because the valve seat is under high thermal stress due to the high-pressure fuel flowing out of the high-pressure fuel accumulator, which has a negative effect on the pressure regulation of the accumulator space. When the pressure regulating valve is screwed onto the base body of the high-pressure fuel accumulator, mechanical stresses occur in the base body and may lead to cracking and fracturing of the material in the area of intersections of connecting bores and the accumulator space in operation of the fuel injection system.
The high-pressure fuel accumulator according to an exemplary embodiment of the present invention avoids the disadvantages known in the related art. Due to the fact that a pressure regulating valve installed in the base body of the high-pressure fuel accumulator is provided, a separate housing part for the pressure regulating valve may be eliminated, thus reducing manufacturing costs for the entire system. Due to the installation of a pressure regulating valve in the base body of the high-pressure fuel accumulator, the complex seals on the pressure regulating valve used in the related art may be unnecessary. Since no screw connections are used in installing the pressure regulating valve in the base body of the high-pressure fuel accumulator, this may reduce material stresses in the transition area between the connecting bores and the accumulator space of the high-pressure fuel accumulator. Therefore, the pressure regulating valve may also be arranged in spatial proximity to the connecting bores, thereby reducing the installation space in the longitudinal direction of the base body. Due to the installation of the pressure regulating valve in the base body of the high-pressure fuel accumulator, thermal stabilization of the valve seat may also be achieved to advantage, because heat may be released from the valve seat to the metal base body.
The pressure regulating valve may be designed as a solenoid valve whose electromagnet is installed in a recess on the end face of the base body and sealed with a cover part.
In another exemplary embodiment, the base body may have a connection for supplying overflow fuel, this connection being connected to the relief space provided in the base body through an inlet line. The valve seat situated in the relief space may be cooled to advantage by supplying overflow fuel, which is at a lower temperature than the fuel in the accumulator space. The overflow fuel washed in through the inlet line flows out through the low-pressure connection together with the fuel flowing out of the accumulator space through the drain channel.
Another exemplary embodiment, in which the relief space, the drain channel from the accumulator space, and a section of a drain line connecting the relief space to the low-pressure connection are designed in a valve part which is inserted into a longitudinal bore in the base body to form the accumulator space and seals this longitudinal bore at one end, may be advantageous. Manufacture of the valve seat and the drain channel, which may contain a throttle, may be easier and less expensive to implement in the valve part. The base body may be provided with a longitudinal bore passing through at least one side. After manufacturing the valve part, it may then be inserted through the open end of the longitudinal bore into the latter and may be connected to the inside of the longitudinal bore with a seal.